During the production of any device, whether it be a simple or a complex device, there always exists the problem of defects. As the device becomes more and more complicated, it becomes more difficult to control the quality of the products being produced. Furthermore, when producing complex items, there will always exist situations some units perform well and other units do not perform as well. Many times this performance variation is due to factors unknown to the producer of the products, or the known problems are not so severe as to warrant drastic measures being taken.
It is always desirable to screen the bad units from the production line at a point as soon as possible to allow the repair of such units. Alternatively, it may be necessary to pull products which are bad performers from the production line and scrap them. As the device becomes more and more complex, the cost of assembly increases. If units having bad performance characteristics can be caught at a point early on the production line, money can be saved by not furthering the assembly of these units. Furthermore, if problems on a production line can be identified at an early point in time, an appropriate solution may be implemented in a timely fashion.
The ring laser gyroscope is a very complex device used in inertial navigation systems to sense inertial rotation. Ring laser gyroscopes are devices well known in the art which utilize counter propagating optical signals to detect rotation. Further information regarding ring laser gyroscopes can be found in U.S. Pat. No. 3,373,650 to Killpatrick. Because of the complexity of the ring laser gyroscope, production can be very costly and time consuming. Furthermore, performance of a ring laser gyroscope is very important. Many times the gyroscope is required to meet exacting specifications which dictate its performance requirements, power consumption requirements and size requirements.
In order to assure the performance and operation of the ring laser gyroscope, it is necessary to test these units at some point in time. Preferably, the units can be tested to determine their performance at a point early in their assembly. In order to test the performance of a ring laser gyroscope, it is necessary to have all functional elements present. These elements include the laser gyro block having mirrors attached thereto on the appropriate corners, appropriate cathode and anode structures to promote lasing of gas contained within the laser gyro block, and a wedge mirror for directing optical signals out of the laser gyro block. Furthermore, readout sensors are required for detecting optical signals directed from the wedge mirror. Lastly, path length control transducers are required to adjust the optical dimensions of the cavity within ring laser gyro block.
One previous method of screening the ring laser gyro during production involved testing of the gyro after it had been fully assembled. As indicated earlier, it is very costly and time consuming to carry out all these steps of assembly. Further, this time and cost may be wasted if the gyro has performance problems caused by processes or parts incorporated into the gyro at an early point of its assembly.
Another method of screening involved checking certain parameters of the gyro as it was being assembled and attempting to predict performance based upon those tested parameters. For example, once the block was assembled to a point that allowed the gas discharge laser to be operated, the laser intensity was tested at various power levels. Predictions as to gyro performance were then made based on these laser intensity measurements.